The present invention relates to improved imageable photoresist laminates for use in abrasion etching applications. More particularly, the invention relates to durable imageable photoresist laminates containing a rhodanine-based crosslinkable resin.
Photosensitive laminate structures have been used for many years to create imageable patterns useful for abrasion etching of substrate materials. The laminates contain photosensitive resins that are crosslinked by actinic radiation. Ultraviolet or visible light is used to imagewise expose these laminates and form a durable image in the laminate structure. The exposed images are subsequently developed to remove unexposed material. Thereafter the laminate is transferred to a substrate surface for selective surface modification, such as by abrasive etching using sandblasting techniques.
One of the main materials used in photoresist laminates is photosensitive resins. Two commonly used types of photosensitive resins are those containing diazonium salts and strylpyridinium salts. Diazonium salt materials, when contacted by ultraviolet light, yield one molecule of nitrogen per diazonium group and generate active crosslinking species. Commonly used diazonium photoinitiated crosslinkers include paradiazodiphenylamine salts. One advantage of diazonium salt compositions is that they undergo a color change upon exposure to actinic radiation. This color change is useful because it provides a printout image that can be used to position the laminate during placement on a substrate.
Although diazonium salt materials are suitable for many photosensitive laminate applications, a need exits for a material that cures more rapidly than diazonium salts. In addition, some diazonium salts show inadequate storage and stability properties. The other common photosensitive resin can include stibazole-containing materials. These stibazole materials may be present in the form of salts of acids such as a hydrochloride, hydrobromide, perchlorate, tetrafluoroborate, phosphate, and sulfate. Styrylpyridinium salt compositions typically have improved curing speed and stability compared to diazonium compositions. However, styrylpyridinium salt compositions usually do not change color to form a print out image, and are therefore often more difficult to position than diazonium compositions. In addition, styrylpyridinium compositions often lack adequate strength and durability for some applications.
A further problem with both of these resin materials, and resin materials in general, is that they sometimes undergo blocking or bricking, in which multiple laminates adhere together during storage. Such undesirable adherence can be a significant obstacle to storing and using the laminate materials.
Therefore, a need exists for improved photosensitive laminates utilizing photoresist resins other than diazonium salts and strylpyridinium salts. Such laminates are preferably fast curing, stable, non-blocking, and produce a print out image upon exposure to actinic radiation. In addition, the laminates should have sufficient mechanical and abrasive strength to withstand erosive exposure, such as exposure to sandblasting materials.
The present invention relates to photosensitive laminates. In specific implementations the invention relates to a photosensitive laminate comprising a carrier or substrate and an imageable photosensitive layer. The laminate may also comprise an intermediate membrane between the photosensitive layer and the carrier material. The photosensitive layer includes a resin containing the following functional unit: 
wherein X is an organic moity and Y is selected from the following groups: 
wherein Z is selected from at least one of lithium, sodium, potassium, ammonium, monoalkylammonium, dialkylammonium, and tetraalkylammonium.
These resin compositions are typically rhodanine-based crosslinkable resins, and include compositions having the functional unit: 
In use, the imageable photosensitive layer structure can be imagewise exposed to actinic radiation to form a durable image which is subsequently developed by aqueous washing to remove unexposed photosensitive resin. This image can then be transferred to a surface for appropriate surface modification, such as by sandblasting.
For the purposes of this application, the term xe2x80x9ccarrierxe2x80x9d and xe2x80x9ccarrier layerxe2x80x9d typically refers to a film or other thin layer upon which the photosensitive layer is formed. The term xe2x80x9csubstratexe2x80x9d typically refers to an object that is modified, blasted, etc., using a process like sandblasting with a mask formed from the photoimaged laminate of the invention. xe2x80x9cImagexe2x80x9d and xe2x80x9cimage transferxe2x80x9d typically refers to the image formed in the photosensitive layer.
The invention can be embodied in various structures. In one structure, the carrier layer is coated with a membrane layer, and the photosensitive layer is applied over the membrane layer. In another structure, a carrier layer is directly coated with the photosensitive layer. These laminate structures can have other functional layers to improve processability, photoimaging, or surface modification.
Additional aspects of the invention are processes for forming an image using the laminate structure of the invention. In one process, the laminate structure is first exposed to actinic radiation, and then developed, processed and transferred to a substrate surface for modification, such as by sand blasting. After the etching or other modification is complete and a pattern is fully formed in a surface of an object, the remaining imaged portions of the laminate can be removed either mechanically or chemically from the surface of the object by gentle cleaning.